As described in WO 2007/099161, glycerol is becoming an abundant chemical product as industry and consumers become increasingly reliant on fuels from biological sources. In particular, fuels (also known as biofuels) are being made from biogenic fat- or oil-containing sources and used oils obtained, for example, from cooking oil waste from restaurants and waste animal fats from food-related processing plants. Diminishing supply of readily available traditional petroleum sources, increasing prices of petroleum feeds and concerns of their impact on the environment are driving increased demands for alternative fuels such as biofuels.
Biogenic oils and fats as they exist per se are not particularly suitable as engine fuel, and therefore require further processing and purification using generally complex processes. These processes, for example, remove lectins, carbohydrates and proteins, also referred to as oil sludge. With some oils, such as rapeseed oil, large amounts of free fatty acids have to be removed.
Biogenic oils processed in this manner differ from conventional diesel fuels in several respects. The former typically have a higher density than diesel fuel, and the cetane number of certain biogenic oils, such as rapeseed oil, is lower than that of diesel fuel. The higher viscosity and lower cetane for these oils lead to an unacceptable deterioration in the oil's fuel properties, which can lead to an engine running less smoothly, thereby increasing noise emission, as well as lead to incomplete combustion in the engine's combustion chamber because of decreased atomization of a more viscous fuel. Incomplete combustion leads to coking, and therefore increased particulate emission.
The above problems can be solved by converting (via transesterification) triglycerides (fatty acid esters of glycerol) present in the biogenic oil and used fats into monoalkyl esters of fatty acids, in particular methyl or ethyl esters. These esters, also referred to as “biodiesel” or FAME, can be used to run diesel engines without major retrofits, and frequently at reduced particulate emissions compared to normal diesel fuel. Conversion of these of triglycerides via transesterification for biodiesel production does result in glycerol (˜10%), however. Transesterification processes therefore can be inefficient due to conversion of the feedstock to a product with little industrial value. There is therefore a need for effective and economical processes, which permit utilization of the glycerol obtained in biodiesel production, especially on an industrial scale.
Processes for hydrogenation of glycerol into usable chemicals are known. Various catalysts have been utilized in these processes, and a number of these catalysts comprise copper.
J. Chaminand et al., in Green Chem. 6, 2004, pages 359-361, describe the hydrogenation of aqueous glycerol solutions at 180° C. and 80 bar hydrogen pressure in the presence of supported metal catalysts based on Cu, Pd and Rh. Copper chromite, copper zinc oxide, copper aluminum oxide and copper silicon dioxide are mentioned as catalysts for such processes. Indeed, it is widely known that copper chromite is a suitable catalyst in the hydrogenation of glycerol. Copper chromite, however, is an oxide that is prone to chemical and physical degradation relative to metallic catalysts.
M. A. Dasari et al., in Appl. Chem. A: General 281, 2005, pages 225-231, describe a process for the low-pressure hydrogenation of glycerol to propylene glycol (1,2-propane diol) at a temperature of 200° C. and a hydrogen pressure of 200 psi (13.79 bar) in the presence of a nickel, palladium, platinum, copper, or copper chromite catalyst.
German Patent 524 101 has been attributed as describing a process, in which glycerol is subjected to a gas-phase hydrogenation in the presence of a hydrogenation catalyst and hydrogen in considerable excess. Copper and/or cobalt catalysts can be used for the hydrogenation of glycerol. See U.S. Pat. No. 7,355,083 and WO 2007/099161.
R. Connor and H. Adkins, in J. Am. Chem. Soc. 54, 1932, pages 4678-4690, describe the hydrogenolysis of oxygen-containing organic compounds, such as glycerol, to 1,2-propanediol in the presence of a copper-chromium-barium oxide catalyst.
C. Montassier et al., in Bulletin de La Societe Chimique de France 1989, No. 2, pages 148-155, describe investigations into the reaction mechanism of the catalytic hydrogenation of polyols in the presence of various metallic catalysts, such as, for example, hydrogenation of glycerol in the presence of copper.
EP 0 523 015 describes a process for the catalytic hydrogenation of glycerol for the preparation of 1,2-propanediol and 1,2-ethanediol in the presence of a Cu/Zn catalyst at a temperature of at least 200° C. In this process, the glycerol is used as an aqueous solution having a glycerol content of from 20 to 60% by weight, the maximum glycerol content in the working examples being 40% by weight.
U.S. Pat. No. 5,616,817 describes a process for the preparation of 1,2-propane diol by catalytic hydrogenation of glycerol at elevated temperature and superatmospheric pressure, in which glycerol having a water content of not more than 20% by weight is reacted in the presence of a catalyst which comprises from 40 to 70% by weight of cobalt, if appropriate, manganese and/or molybdenum and a low copper content of from 10 to 20% by weight. The temperature is in the range of from about 180 to 270° C. and the pressure in a range of from 100 to 700 bar, preferably from 200 to 325 bar.
US 2008/0045749 discloses a two step process in manufacturing 1,2 propane diol from glycerol in which the glycerol is first subjected to a dehydrogenation reaction to produce a carbonyl compound, hydroxyacetone. The second step can comprise hydrogenating the acetone to 1,2-propane diol. It is mentioned that a promoted skeletal copper metal catalyst can be used in this second step. This process is complicated and specifically designed to accommodate manufacturing a second alternative compound from the acetone, in particular, manufacturing amino alcohol from an amine adduct of the acetone.
Other types of catalyst for hydrogenation of glycerol include acid resin catalysts (e.g, resins sold as Amberlyst® resins) in combination with hydrogenation catalysts, but there is need to find improved and more efficient catalysts for converting this increasingly abundant material into a useful product. Its use is more easily adopted when the product is relatively free of byproduct, e.g., 1,2-ethane diol, (“ethylene glycol” or “EG”) and the process for manufacturing the 1,2 propane diol (“propylene glycol” or “PG”) is more economical when the process is more selective for the desired diol and feedstock is not lost during the conversion. It would also be helpful if the processes for manufacturing the product involved less expensive processing conditions such as being operated in the liquid phase. There is the general problem, in delivering organic feed to a fixed bed reactor, of evenly distributing the feed radially across the reactor, i.e. across the diameter of the reactor bed. Vapor phase reactions, i.e., those in which the reactants are in the vapor phase, provides for even distribution, but using such phase reactors requires addition of equipment extraneous to the reactor, i.e., a vessel to heat and vaporize the glycerol and then sweep it into the reactor/catalyst bed with hydrogen. See U.S. Pat. No. 7,355,083. Such processes have been shown to achieve relatively good selectivity results for manufacturing 1,2 propane diol, but at a relatively higher cost. Vapor phase reactors not only require additional equipment, but also operate at relatively high temperatures, high ratio of hydrogen to feedstock, and lower throughput. Liquid phase reactions, on the other hand, pushes liquid through the reactor via a relatively inexpensive pump to move a thin film of liquid reactant(s) over the catalyst (“trickle bed” processes). These processes do not involve addition of equipment extraneous to the reactor. Liquid phase reactions have also been shown to evenly distribute reactant across catalyst, and at relatively good throughput. Good selectivity of 1,2 propane diol using such reactions however have not yet been seen.